MIP (Mobile IP) is under consideration as a scheme for providing mobility to a mobile station in an IP network. According to MIP, the mobile station uses two IP addresses: a home address and a care-of address, to continue communications. The home address is a permanent IP address allocated to the mobile station in the IP network. The care-of address is assigned according to an IP address configuration scheme such as DHCP (Dynamic Host Configuration Protocol). When the mobile station receives the care-of address, the mobile station reports the care-of address as Binding Update to a mobility anchor apparatus (home agent). The mobility anchor apparatus manages the correspondence between the home address and the care-of address and continues communications with the mobile station using the care-of address. According to MIP, since the mobile station controls the change of the path due to its mobility, a bearer for the mobile station is not established in the network.
In a mobile communication network, on the other hand, the bearer for the mobile station may be established in the network for the purpose of the change of the path. For example, in a network to which GTP (GPRS Tunneling Protocol) or PMIP (Proxy Mobile IP) is applied, the bearer for the mobile station is established in the core network (see 3GPP TS23.401 and TS23.402). As used herein, the bearer is a communication path which is established to transmit user data. Each bearer is defined by its properties such as communication quality.
FIG. 1 shows an example of such a mobile communication system. Typically, the mobile communication system has a layered structure including a core network and an access network. The core network is mainly responsible for call control and service control, while the access network controls or terminates the radio technology or the wired technology. The core network includes a mobility anchor apparatus 10 which achieves mobility as call control such as handover by switching different access networks. For example, when the mobility anchor apparatus 10 receives user data from an external network, the mobility anchor apparatus 10 switches access networks according to the location of the mobile station 30 to relay the user data to the mobile station 30. According to GTP and PMIP, the core network includes access apparatuses 20 at the edges of the core network. The access apparatus 20 is responsible for connection control when the mobile station 30 connects to the access network. According to GTP and PMIP, bearers are established between the mobility anchor apparatus 10 and access apparatuses 20.
When the mobile station 30 communicates in the access network to which PMIP is applied, the mobile station 30 transmits a path switching signal (Proxy Binding Update) to the access apparatus 20, as is the case with MIP. Upon receiving the path switching signal, the access apparatus 20 transmits a bearer establishment signal. When the bearer is established, the mobility anchor apparatus 10 switches to an appropriate access network. When the mobile station 30 communicates in the access network to which GTP is applied, the path is established basically in the same manner as in the access network to which PMIP is applied.